Method and composition for stabilizing incompetent oil containing formations



United States Patent 3,429,373 METHOD AND COMPOSITION FOR STABILIZING INCOMPETENT OIL CONTAINING FORMATIONS Bobby G. I-Iarusberger and Joy T. Payton, Houston, Tex

assignors to Texaco Inc., New York, N.Y., a corporation of Delaware 1 No Drawing. Continuation-impart of application Ser. No. 597,532, Nov. 29, 1966. This application Apr. 24, 1968, Ser. No. 723,935 US. Cl. 166-276 12 Claims Int. Cl. E21b 43/02, 33/13; C04b 7/00 ABSTRACT OF THE DISCLOSURE Method of treating an oil-containing incompetent formation to prevent the movement of unconsolidated sand particles in a well bore by forming a slurry of sand, cement and a sufiicient amount of a petroleum oil fraction containing an oil wetting agent therein to oil wet the sand and cement particles, suspending the oil wet sand and cement particles in an aqueous carrier medium, injecting the aqueous suspension against the unconsolidated formation at a pressure effective to force the suspension into the unconsolidated formation, contacting the suspension with an aqueous surface active agent solution to water wet the cement particles, permitting the cement to set and form a permeable cement and recovering oil through the cement.

This is a continuation-in-part application of application Ser. No. 597,532, filed Nov. 29, 1966, now abandoned.

The present invention relates to the treatment of permeable underground formations. More particularly, the present invention relates to a method of treating permeable underground oil and/or gas containing formations to stabilize the sandy portion thereof and to a treating composition useful in the stabilization of incompetent sand containing underground formations.

The recovery of fluids such as gas and/or oil from underground formations has been troublesome in areas wherein the underground formation is composed of one or more incompetent sand containing layers or zones. The sand particles in the incompetent zone and/or layer tend to move or migrate to the well bore during recovery of the formation fiuids from the particular zone and/or layer and frequently the moving sand particles block the passageways leading to the well bore. Plugging or materially impairing the flow of the formation fluids toward the bore hole results in a loss of these fluids to the producer or so decreases the rate of oil recovery from the well as to cause the well to be shut down because it is economically unattractive to continue to produce therefrom. An additional adverse factor resulting from the movement of the sand particles toward the well bore is that they are often carried along with the formation fluids to the well bore and passed through the pipes, pumps, etc. being used to recover the formation fluids to the surface with resulting damage to the moving parts thereof as the sand particles are very abrasive.

Many attempts have been made heretofore to prevent or decrease the flow of undesirable sand particles in the formation and/or in the production tubing and associated equipment, such as by the placement of sand screens, filters, liners and so forth. These prior attempts have been unsuccessful for a number of reasons among which is that these mechanical devices fail to prevent completely the flow of the formation'particles into the production equipment. In addition these devices interfere with various types of completion and workover operations. In recent years, the industry has attempted to avoid the difiiculties 3,429,373 Patented Feb. 25, 1969 encountered in the use of mechanical devices by employing various chemical compositions to effect consolidation of the underground incompetent formations. These methods have generally consisted of injecting into the underground formation polymerizable resinous materials which when subsequently polymerized form permeable barriers in the formation to prevent the sand particles from movement therethrougb. However, this technique of sand consolidation has not met with wide-spread acceptance because of the inherent difficulties of effecting polymerization of the resinous materials in the formation to a degree suificient to consolidate these underground formations and yet permitting the unobstructed flow of the desirable formation fluids therethrougb. Further, the cost associated with these resin coating methods has been relatively high in comparison with the prior mechanical methods.

By the method of the present invention one is able to treat effectively the underground formation to be stabilized in a rapid and eificient manner while avoiding the disadvantages of these prior art methods both mechanical and chemical.

One object of the present invention is to provide an improved method of treating underground sand containing formations to stabilize the incompetent formation. An additional object is to provide a fluid permeable barrier between the formation sand and the well bore to prevent or to minimize the flow of unconsolidated sand particles therethrough while maximizing the flow of desired fluids and particularly petroleum hydrocarbons therethrough. A still further object is to provide a novel treating composition for use in stabilizing incompetent sand formations and to a method of placing same to form a permeable cement filter against the incompetent formation.

How these and other objects of the invention are accomplished will become apparent with reference to the accompanying disclosure. In at least one embodiment of the method of this invention at least one of the foregoing objects will be obtained.

It has now been discovered that an improved method of treating an incompetent sand containing underground formation comprises introducing against said formation a particular treating composition consisting essentially of a hydrocarbon oil wet sahd and cement slurry dispersed or suspended in an aqueous carrier medium in an amount suflicient to stabilize the formation and then to contact the introduced slurry with an aqueous solution of a hydrophilic surfactant to penetrate the oil layer about the sand and cement components of the slurry and to effect setting of the cement to form a fluid permeable barrier film between the formation and the well bore. The resultant formed permeable cement barrier serves to prevent -or to materially reduce the flow of the unconsolidated sandy particles therethrough while permitting the flow of desirable formation fluids through the permeable barrier at a substantially unimpaired rate.

In carrying out the method of the present invention the permeable cement slurry suspended in the aqueous carrier medium is pumped down the well bore under sufficient pressure to force the hydrocarbon oil wetted sand-cement slurry against the unconsolidated formation adjacent to or in reasonable proximity to the well bore. When the permeable cement slurry is placed against the formation to be consolidated the slurry then is contacted with an aqueous solution of a hydrophilic surfactant which displaces the oil layer around the sand cement particles and renders these particles water wet. The cement component of the slurry then sets up and hardens. After the cement hardens the well can be equipped for production and the formation fluids can be recovered by passing through the resulting formed permeable cement barrier into the well bore and recovered therefrom without the formation fluids being contaminated with the presence therein of unconsolidated sand particles.

The method of the present invention is particularly adaptable for use in any type of well completion but is generally used in a well wherein casing has been set and which has perforations therein at the desired intervals behind which the unconsolidated formation sands are located. Packers can be initially set above and below the perforated intervals to prevent the permeable cement slurry from passing into the non-isolated portions of the well and also to permit build-up of sufficient pressures on the slurry to force same through the perforations and against the formation without plugging up the well bore. After the permeable cement slurry has been forced through the casing perforations and against the formation and after it has been contacted with the aqueous solution of the hydrophilic surfactant the well is closed in to permit the cement to set and form the permeable cement barrier for the unconsolidated sand in the formation.

The slurry composition useful in the method of the present invention must meet certain specific requirements. The sand component in general should be closely sized in the broad range 12-80 mesh, i.e. 12-20, 20-40, 40-60 or intermediate meshes, to permit effective relatively high permeability cement barriers being formed. In addition, the ratio of the sand component to the cement component prior to the sand and cement being wetted by the hydrocarbon oil component of the slurry should be about 3 parts to about 12 parts by weight of sand per part of cement. It has been found that a frac. sand, i.e. a sand customarily used in formation fracturing operations, having a size of between about 20 and 40 mesh is most suitable for use in the cement slurry of the present in-. vention. It is preferred to use a graded sand with the larger grains being not more than about twice the diameter of the smaller grains, i.e. 12-20 mesh, 20-40 mesh, 40-60 mesh, etc. In general, a 20-40 mesh sand is used because of its ready availability and adaptability for use in stabilizing most formations. In addition, the use of a 20-40 mesh sand appears to prevent premature bridging which is likely to be more prevalent with finer mesh sands. Sand particles which are coarser than about 12 mesh and finer than about 80 mesh are unsuitable for use in the composition of the present invention. The coarser particles are not satisfactory because the resultant set cement barrier has too great a permeability to prevent the flow of very fine unconsolidated sand particles therethrough when the well is placed on production. Very fine sand particles, that is those sand particles finer than about 80 mesh, are unsuitable because the resultant set cement has too low a permeability to permit the flow of desired formation fluids therethrough.

The cement component of the composition of the present invention should be present in the dry mixture in a ratio of about 1 part of cement to from 3 to about 12 parts by weight of sand, on a weight basis. The cement component of the composition of the present invention may be any of the cements normally used in oil well cementing operations as well as plaster of paris cement. It is preferred that the cement component be a light weight portland cement having a density of about 75 pounds per cubic foot and a chemical analysis approximately as follows: silicon dioxide 38.3%, aluminum oxide 13.0%, ferric oxide 5.2%, calcium oxide 35.7%, magnesium oxide 1.6% and sulfur trioxide 2.4%, with a loss on ignition of approximately 3.3%. This particular light weight portland cement has been found to be most suitable in the composition of the present invention since permeable cements made from this cement are most stable to attack by formation brines containing sodium chloride or sodium sulfate. Other oil well cements are not as resistant to attack by formation brines or sulfate solutions and therefore are not as practical for use in the cement composition of the present invention. These other cements appear to lose some of their compressive strength and become eroded from contact with sodium chloride and sodium sulfate solutions. In contrast the cements of the composition of the present invention are very resistant to erosion by sodium chloride or sodium sulfate solutions and do not lose their compressive strengths even after prolonged exposure thereto.

The hydrocarbon oil component of the slurry should be employed in an amount of from about 0.4 part to about 0.8 part by weight per part by weight of cement. It is preferred that the oil component be employed in an amount of about 0.5 to about 0.6 part by weight per part by weight of cement. Use of the oil component in this amount provides sufficient oil to wet the cement and sand components of the slurry and at the same time avoids an excess thereof which could possibly damage the unconsolidated underground formation when the slurry is placed adjacent thereto.

Suitable hydrocarbon oils include the kerosene and diesel oil fractions of a petroleum crude oil.

A necessary component of the petroleum oil fraction of the composition of the present invention is an oil wetting water repellant agent, i.e. a water insoluble oleophilic nonionic material of relatively high molecular weight which will permit the petroleum fraction to oil wet the surfaces of the sand and cement particles in the oil slurry. The oil wetting agent must contain an oleophilic group and a polar group for preferential adsorption on or at the oil and sand-cement interfaces. Representative oil wetting agents useful in the practice of the present invention include the relatively high molecular weight amines such as for example, the C -C hydrocarbylamines, decyl-, dodecyland octadecylamine, the C -C fatty alcohols such as cetyl and octadecyl alcohol, the C -C alkylated phenols and naphthols, natural fatty materials such as lanolin, lard, cottonseed oil and fatty acid glycerides, amides such as the C -C fatty acid amides, and mixtures of these oil wetting agents.

'The oil wetting agent is used in an amount of from about 1 to about 10% by weight, based on the weight of the cement particles in the slurry.

The aqueous carrier medium containing the suspended oil wet sand and cement solids is pumped down the well bore and into the formation to be consolidated at a rate of from about 1 to 4 barrels of the suspended solids in the carrier medium per minute. Such pumping rates have been found to give the most satisfactory results in the practice of the invention.

,An aqueous surface active agent solution contacts the emplaced oil wetted sand-cement particles to displace the oil therefrom and to initiate hardening of the cement. The surface active agent used must be a water soluble material to penetrate the oil-sand-cement interface and water wet the cement particles and remove the oil therefrom. Representative surface active agents that will perform satisfactorily in the present invention include anionic, cationic and nonionic materials such as the alkyl,

or alkaryl sulfates and sulfonates, the sulfated and sulfonated alkyloxyated amides, esters or ethers, hydrocarbylamine salts, esters or ether-esters of natural fats and oils, or alkyl phenols. The surface active agents include polyoxyethylene sorbitan-monolaurate, -monopalmitate and -monooleate, oxyalkylated amyl phenol, alkaryl polyether alcohols and polyoxyethylene ether. A preferred surface active agent is an ethoxylated nonylphenol containing about 9.5 moles of ethylene oxide, known by the trade name Surfonic N-95.

Example I A mixture of 700 grams by weight of a frac. sand known by the trade name Ottawa" having a particle size of 20-40 mesh and 140 grams of a hydraulic cement known by the trade name Trinity Lite Wate Cement was prepared by intimately mixing the sand and cement. There was added to the mixture with stirring ml. of a kerosene fraction containing by volume of dodecylamine. The resulting stirred mixture of oil wet solids was suspended in about 2500 ml. of water. The suspension of oil wet solids in the aqueous carrier was pumped at a pressure of 10-50 p.s.i.g. into a test cell measuring 3 inchesin diameter by 6 inches in length. The cell was about half filled with packed sand particles having a mesh size of 70-300. Theoil wet sand-cement mixture was filtered out of the aqueous carrier liquid. Thereafter the sand pack was treated with 500 ml.-of a water solution containing 5 ml. or an ethoxylatednonylphenol having an average of 9.5 ethylene oxide-groups surface active agent known by the tradename Surfonic N-95. The

" these materials.

4. A method as claimed in claim 2 wherein said oil wetting agent is a hydrocarbyl amine containing 12-18 carbon atoms.

surface active agent in the water displaced the oil from the sand-cement particlesfin the pack and hydrated the cement. A hardened cement resulted after a 24 hour waiting-on cement period. The water permeability of the hardened cement was. found to be about 7.darcies which was sufficient to block flow of very fine sand particles f particles having a mesh size of from about 20 mesh to therethrough.

Example 11- 1400 g. of a 20-40 mesh frac. sand were mixed with 255 g. of a hydraulic cement known by the trade name Trinity Lite Wate. 300 g. of the sand/cement mixture were then mixed with 22 cc.- of a 10% solution of dodecylamine in a commercial motor oil having a viscosity index of 75 and an API gravity of 24. The-oil 'is a blend of a'- refined parafiin base distillate and .residual' fractions and contained minor amounts of conventional lubricating motor oil additive suchasa pour depressant,'a detergent,

antioxidant, etc. The oil wet;solids,were then placed in a: I

large container and covered with about 2 liters of fresh water. A pump was then used to pick up a mixture of I r oil wet solids and water andforce this mixture into a 3" x 6" test cell that had been previously partly filled with 70-170 mesh sand. The oil wet solids filtered out against the sand in the cell while the water passed through. After the cell was packed with oil wet solids, the water present in the cell was displaced with400 cc. of a 1%,aqueous solution of the wetting agent known by the trade name .Surfonic M-95." The .surfactant saturated -cell was then placed in a water bath at 140-160 F. and allowed to set overnight. The next day a water flush and other tests of the cell contents showed that the oil wet materials had been converted into a solid mass of high permeability and of about 1200 p.s.i. compressive strength.

Obviously, many modifications and variations of the invention as hereinbefore set forthmay be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method of treatingan oil-containing incompetent formation penetrated by a well bore to prevent the movement of unconsolidated sand particles from said incompetent formation to the well bore as the oil is recovered from said formation which comprises forming a slurry of sand, cement, and sufiicient amount of a petroleum oil fraction containing an oil wetting agent therein to oil wet the sand and cement particles, suspending the resulting oil wetted sand and cement particles in an aqueous carrier medium, injecting said aqueous suspension against the unconsolidated formation at a pressure suflicient to force theaqueous suspension into the unconsolidated formation, contacting the aqueous suspension with an aqueous surface active agent solution to water wet the cement particles, permitting the cement to set to form a permeable cement, and recovering oil from said formation through the formed permeable cement.

5. A method as claimed in claim 4 wherein said primary amine is dodecylamine.

6. A method as claimed in claim 1 wherein said surface'active agent is an ethoxylated nonylphenol containing an average of about 9.5 ethylene oxide groups.

7. A method as claimed in claim 1 wherein the slurry consists essentially of from 3 to 12 parts by weight of sand about mesh from about 0.01 to about 0.10 part by weight of oil wetting agent and from 0.40 to 0.80 part by weight of a petroleum oil fraction, each per part by weight of cement particle.

8. A method as claimed in claim 1 wherein the slurry is suspended in the aqueous carrier medium in an amount of from about 1 to 5 pounds of the slurry per gallon of I the carrier medium. -30.

9. Amethod as claimed in claim 1 wherein the petroleum oil fraction is a kerosene fraction.

10. A method as claimed in claim 1 wherein the petroleum oil fraction is a diesel oil fraction.

11. A method as claimed in claim 1 wherein the unconsolidated formation is washed with salt water fraction to" remove at least a portion of the unconsolidated sand particles adjacent to the well bore and to form a cavity in said unconsolidated formation prior to injection of the aqueous suspension of the oil wetted sandcement particles against said formation.

12. Asand-cement slurry suspended in an aqueous medium fraction for use in forming a permeable cement barrier film in a sand-containing, unconsolidated-oil producing formation which comprises from about 3 to about 12 parts by weight of sand particles having an average mesh size of from about 20 mesh to about 80 mesh, from 0.01 to about 0.10 part by weight of an oil wetting agent, and from 0.40 to 0.80 part by weight of a petroleum oil fraction, each per part by weight of cement, said slurry being present in an amount of from about 1 to 5 pounds per gallon of the aqueous medium.

References Cited UNITED STATES PATENTS 

